Lecture 13 Flashcards
Factors that determine heat rate of heat production
BMR, muscle activity (shivering), thyroxin, norepinephrine/epinephrine, increased cellular chemical activity, extra metabolism for digestion, absorption, and food storage
Factors that determine rate of heat loss
How rapidly heat can be conducted from body core to skin, how rapidly heat can be transferred from skin to surroundings
Mechanisms to increase body temperature
Skin vasoconstriction, piloerection, increase in thermogenesis (shivering, metabolic pathways, thyroxin secretion)
List and describe mechanisms through which heat is lost from the skin
Radiation: loss in the form of infrared heat rays, radiated by all objects not at absolute zero; if temperature of body is greater than ambient temperature, more heat is radiated from the body than to the body
Conduction: kinetic energy of the molecules of the skin is transferred to the air if the air is colder than the skin
Convection: removal of heat from the body by convection air currents
Insensible perspiration: occurs at a rate of 600-700 ml/day; causes a continual heat loss at a rate of 16-19 calories/day
Compare concentrations of constituents of sweat when flow of precursor through the duct is low (slight stimulation of glands) versus rapid (strong stimulation)
Slight stimulation: Na+ = 142 mEq/L and Cl- = 104 mEq/L; similar to that of plasma w/o proteins
Strong stimulation: Na+/Cl- = 50-60 mEq/L with little water reabsorbed
What effect does aldosterone have on sweat composition?
Increases the concentrations of Na+
Describe the anterior pre-optic and pre-optic areas of the hypothalamus and their role in controlling body temperature
Anterior pre-optic hypothalamus: contains warm-sensitive (increase firing rate 2-10X in response to a 10 degree C increase in body temperature) and temperature insensitive neurons (temperature set point is function of the activity of the warm-sensitive neurons)
Posterior hypothalamus: cold-sensitive (increase firing rate when temperature falls)
Where is the primary motor area for shivering located? What is its relationship with the anterior hypothalamic preoptic area? Under what conditions is this area activated?
Dorsomedial portion of the posterior hypothalamus; inhibited by signals from heat center in anterior hypothalamic preoptic area; excited by cold signals from skin and spinal cord
Define chemical thermogenesis and explain how it is related to epinephrine/norepinephrine and brown fat
Increase rate of cellular metabolism due to sympathetic stimulation (epi/norepi); uncouples oxidative phosphorylation; degree of thermogenesis is directly related to amount of brown fat (found in intercapsular space in infants)
Define fever and explain how pyrogens relate to the hypothalamic thermostat set point
Body temperature above the usual range of normal; pyrogens increase set-point temperature by increasing production of IL-1, TNF, IL-6, and INF in phagocytic cells
Explain how the following affect fever: IL-1, prostaglandins, and aspirin
IL-1: Increases set point temperature
Prostaglandins: Increases set point temperature
Aspirin: Decreases set point temperature by inhibiting cyclooxygenase which results in decrease in production of prostaglandins
What is critical body core temperature?
37.1 C (98.8 F)
How does the core body temperature relate to heat loss and heat production?
Heat loss is greater at temperatures above this temperature and heat production is greater at temperatures below this temperature
What is the “set-point” of the temperature control mechanism?
Level at which sweating begins or shivering begins in order to return to critical core body temperature
What happens in the hypothalamus when the core temperature is below/above set point?
Below: posterior hypo activates heat-generating mechanisms
Above: anterior hypo activates heat loss mechanisms
